1. Field of the Invention
Heat-stable, electrically-conductive, thermoplastic, polymeric materials have long been sought. Sheets of such electrically conductive polymeric materials have been made using polyimide as a heat-stable matrix and finely-divided carbon as a conductive filler. It has often been the case that the interior of carbon-filled polyimide articles exhibits adequate, relatively high, electrical conductivity; but the surface of the articles exhibits very low conductivity. There are uses for electrically conductive polyimide wherein a high volume conductivity is required and uses wherein only a high surface conductivity is required.
2. Description of the Prior Art
Canadian Pat. No. 708,896 discloses that polyimide articles can be made with a carbon particle filler to yield electrical conductivity. British Pat. No. 2,103,633 discloses that polyimide articles having an electrically-conductive filler can be used in combination with metallic circuit configurations in the assembly of compound electrical devices such as printed circuit boards. Neither the Canadian patent nor the British patent contains disclosure relating to increase of electrical conductivity by treatment of the polyimide surface of those articles. Polyimide articles have been etched, using basic compounds, to increase adhesive bond strengths and to create perforations for uses such as in electronic circuitry manufacture.
U.S. Pat. Nos. 3,361,589; 3,871,930; 4,039,371; and 4,426,253 all disclose polyimide etching by a broad range of basic etchant materials. There is no disclosure of etching conductor-filled polyimide articles.
Polyimide articles have also been etched in the direct production of electrically conductive parts. U.S. Pat. Nos. 3,395,057; 3,457,537; 3,546,011; and 3,821,016 all disclose chemical milling of polyimide articles to expose solid, large-area, bodies of metallic electrical conductors.